Optical disk apparatus for mechanically restricting the distance between an optical disk and an optical head

ABSTRACT

An optical disk cartridge and an optical disk apparatus wherein, whether or not an optical disk has a different thickness, the distances of a pair of optical heads to a pair of recording faces of the optical disk can be set readily with a high degree of accuracy. The optical disk cartridge comprises a cartridge including a pair of halves between which an optical disk is accommodated for rotation, and a sample plate having a thickness corresponding to the thickness of the optical disk and disposed in parallel to the optical disk at a position in the cartridge in which the sample plate does not interfere with the optical disk. A pair of restricting elements are provided in the optical disk apparatus and contacts, when the optical disk cartridge is loaded, with the opposite surfaces of the sample plate to mechanically restrict the distances of the optical heads from the recording faces of the optical disk.

This is a continuation of co-pending application Ser. No. 08/044,577filed on Apr. 7, 1993, now abandoned, which, in turn, is a divisional ofapplication Ser. No. 07/840,512 filed on Feb. 24, 1992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical disk cartridge in which an opticaldisk having a pair of recording faces formed on the opposite surfacesthereof is accommodated and also to an optical disk apparatus forrecording and/or reproducing such optical disk.

2. Description of the Prior Art

An optical disk apparatus is conventionally known wherein an opticaldisk having a pair of recording faces formed on the opposite upper andlower surfaces thereof is placed in position on a turntable and therecording faces of the optical disk are recorded and/or reproduced bymeans of a pair of upper and lower optical heads.

In an optical disk apparatus of the type mentioned, a spot of a laserbeam is irradiated upon a recording face of an optical disk by means ofan objective lens of an optical head to effect recording (writing) orreproduction (reading) of information to or from the recording face.Accordingly, recording or reproduction of an optical disk is difficultif the distances of the upper and lower optical heads to the upper andlower recording faces, respectively, of the optical disk (here, suchdistances are equivalent to the focal lengths of spots of laser beams)are not set with a high degree of accuracy so that the spots may befocused on the recording faces of the optical disk.

Meanwhile, the thickness of a disk cartridge for such optical disk isspecified In the national or international standards. However, since anoptical disk is normally formed from a glass base plate, a plastic baseplate or the like and has a different structure depending upon amaterial used, it may have a different thickness depending upon thematerial used.

Meanwhile, in an optical disk apparatus of the type described above, thedistances of the upper and lower optical heads to the upper and lowerrecording faces, respectively, of the optical disk are set withreference to a height or vertical position of a turntable of a spindlemotor on which the optical disk is received.

Accordingly, when the optical disk received on the turntable has adifferent thickness, the distance particularly of the upper optical headto the upper recording face of the optical disk is different from aspecified distance, and consequently, recording or reproduction by theupper optical head may be difficult or impossible.

Thus, an optical disk apparatus has been developed wherein a head basefor the upper optical head is adjusted upwardly or downwardly under theservoing control of a motor in order to optimize the distance of theupper optical head to the upper recording face of an optical disk inaccordance with a dispersion in thickness of the optical disk.

Such solution of adjusting the head base of the optical head upwardlyand downwardly in accordance with a dispersion in thickness of anoptical disk under the servoing control of the motor to set the distanceof the optical head to the recording face of the optical disk as in theconventional optical disk apparatus described just above, however, isdisadvantageous in that the mechanical and electric (a servo circuit isrequired) constructions are very complicated and besides the speed uponsuch setting is low and the reliability in setting is low.

SUMMARY OF THE INVENTION

It is an object of the present Invention to provide an critical diskcartridge and an optical disk apparatus wherein, whether or not anoptical disk has a different thickness, the distances of a pair ofoptical heads to a pair of recording faces of the optical disk can beset readily with a high degree of accuracy.

In order to attain the object, according to an aspect of the presentinvention, there is provided an optical disk cartridge, which comprisesan optical disk having a pair of recording faces formed on the oppositesurfaces thereof, a cartridge including a pair of halves between whichthe optical disk is accommodated for rotation, and a sample plate havinga thickness corresponding to the thickness of the optical disk anddisposed in parallel to the optical disk at a position in the cartridgein which the sample plate does not interfere with the optical disk.

With the optical disk cartridge, the thickness of the optical disk canbe detected readily with a high degree of accuracy with reference to thesample plate having a thickness corresponding to the thickness of theoptical disk. Accordingly, even if the optical disk has a differentthickness, the distances of a pair of optical heads of an optical diskapparatus to the recording faces of the optical disk can be set readilywith a high degree of accuracy each time an optical disk cartridge isloaded In position into the optical disk apparatus.

According to another aspect of the present invention, there is providedan optical disk apparatus, which comprises a turntable of a spindlemotor for removably receiving thereon an optical disk which has a pairof recording faces formed on the opposite surfaces thereof, a sampleplate having a thickness corresponding to the thickness of the opticaldisk, means for receiving the sample plate in parallel to the opticaldisk at a position at which the sample plate does not interfere with theoptical disk, a pair of optical heads mounted for relative movementtoward the recording faces of the optical disk received on theturntable, and a pair of restricting means for contacting with theopposite surfaces of the sample plate received at the position tomechanically restrict the distances of the optical heads from therecording faces of the optical disk.

According to a further aspect of the present invention, there isprovided an optical disk apparatus. which comprises means for removablyloading in position an optical disk cartridge in which an optical diskhaving a pair of recording faces formed on the opposite surfaces thereofis accommodated for rotation and which has a sample plate having athickness corresponding to the thickness of the optical disk anddisposed at a position at which the sample plate does not interfere withthe optical disk, a turntable of a spindle motor for removably receivingthereon the optical disk in the optical disk cartridge loaded inposition, a pair of optical heads mounted for individual relativemovement toward the recording faces of the optical disk received on theturntable, and a pair of restricting means for contacting with theopposite surfaces of the sample plate of the optical disk cartridge tomechanically restrict the distances of the optical heads from therecording faces of the optical disk.

With the optical disk apparatus, the distances of the optical heads tothe recording faces of the optical disk in the optical disk cartridgeloaded in position are mechanically restricted by contacting the pair ofrestricting means with the opposite surfaces of the sample plate havinga thickness corresponding to the thickness of the optical disk.Accordingly, even if the optical disk has a different thickness, thedistances of the optical heads to the recording faces of the opticaldisk can be set readily with a high degree of accuracy each time anoptical disk cartridge Is loaded In position into the optical diskapparatus. Besides, such setting can be performed at a high speed In ahigh reliability with a simple structure.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description and theappended claims, taken in conjunction with the accompanying drawings inwhich like parts or elements are denoted by like reference characters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational sectional view of an optical disk cartridgeand an optical disk apparatus showing a preferred embodiment of thepresent invention;

FIG. 2 is a similar view but showing the optical disk cartridge andoptical disk apparatus when an optical disk having a different thicknessis loaded;

FIG. 3 is a plan view of the optical disk cartridge:

FIG. 4 is a side elevational view of the optical disk cartridge:

FIG. 5 is an enlarged sectional view showing a sample plate of theoptical disk cartridge;

FIG. 6 is a similar view but showing a modification to the sample plateof FIG. 5;

FIG. 7 is a sectional view showing a positioning hole in the modifiedsample plate of FIG. 6:

FIG. 8 is a side elevational view, partly in section, showing theoptical disk apparatus of FIG. 1:

FIG. 9 is a side elevational view, partly in section, showing an opticaldisk cartridge mounting apparatus of the optical disk apparatus;

FIG. 10 is a front elevational sectional view of the optical diskcartridge mounting apparatus;

FIG. 11 is a horizontal sectional view of the optical disk cartridgemounting apparatus;

FIG. 12 is a side elevational view, partly in section, showing achucking plate and a lifting apparatus for an upper optical head blockof the optical disk cartridge mounting apparatus; and

FIG. 13 As a plan view of the lifting apparatus for the upper opticalhead block.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIGS. 1 and 2, there is shown an optical diskcartridge and an optical disk apparatus to which the present inventionis applied. The optical disk cartridge generally denoted at 1 includes acartridge 2 composed of a pair of upper and lower halves 2a and 2b, andan optical disk 3 accommodated for rotation in the cartridge 2. Theoptical disk 3 has a pair of recording faces 3a and 3b formed on theopposite upper and lower surfaces thereof. The upper and lower halves 2aand 2b of the cartridge 2 have a pair of upper and lower openings 4a and4b formed therein, respectively. Each of the upper and lower openings 4aand 4b is in the form of an elongated hole and serves both as aturntable admitting hole and as a head admitting hole. A sample plate 5having a circular shape or the like and having a thickness S2corresponding to the thickness S1 of the optical disk 3 (for example.S1=S2) is provided adjacent an outer periphery of and in parallel to theoptical disk 3 in the cartridge 2 such that it may not interfere withthe optical disk 3. The upper and lower halves 2a and 2b have a pair ofupper and lower small circular openings 6a and 6b formed therein in anopposing relationship to upper and lower faces 5a and 5b of the sampleplate 5.

When the optical disk cartridge 1 is loaded in position into the opticaldisk apparatus 8, a turntable 10 securely mounted horizontally at thetop end of a spindle 9a of a spindle motor 9 is relatively inserted frombelow into the cartridge 2 through the lower opening 4b, whereupon theoptical disk 3 is fitted at a center hole 3c thereof with a center hub10a of the turntable 10 so that it is received horizontally at an upperface 10b of the turntable 10. Then, upon such loading of the opticaldisk cartridge 1, the sample plate 5 is positioned together with theoptical disk 3 to a position in the optical disk apparatus 8 at which itdoes not interfere with the optical disk 3. It is to be noted that, inthis instance, the cartridge 2 is received horizontally on a pluralityof height reference pins 11 some of which are formed as positioningpins.

The optical disk apparatus 8 includes a pair of upper and lower opticalheads 13a and 13b having objective lenses 12a and 12b, respectively, apair of upper and lower restricting elements 15a and 15b in the form ofvertical pins mounted on optical head bases 14a and 14b of the opticalheads 13a and 13b and extending in the vertically opposite directions,respectively, a chucking plate 16, and so forth. When the optical diskcartridge 1 is loaded in position into the optical disk apparatus 8, thelower optical head 13b is relatively inserted from below into the loweropening 4b so that the objective lens 12b thereof comes to a position ata distance L2 from the lower recording face 3b of the optical disk 3. Itis to be noted that, after the optical disk cartridge 1 is received inposition, the chucking plate 16 is inserted from above into the upperopening 4a so that it is fitted with an inner periphery of the centerhole 3c of the optical disk 3 from above in the direction indicated byan arrow mark a and presses the optical disk 3 against the upper surface10b of the turntable 10 to hold the optical disk 3 against the turntable10.

Further, when the optlcal disk cartridge 1 is loaded, the lowerrestricting element 15b is relatively inserted from below into the lowersmall opening 6b and contacted perpendicularly with the lower surface 5bof the sample plate 5.

After the optical disk cartridge 1 is loaded, the upper optical head 13aand upper restricting element 15a are moved down together with eachother in the direction indicated by the arrow mark a by the upperoptical head base 14a so that the upper restricting element 15a isinserted from above into the upper small opening 6a and contactedperpendicularly with the upper surface 5a of the sample plate 5 whilethe upper optical head 13a is inserted from above into the upper opening4a so that the objective lens 12a thereof comes to a position at adistance L1 from the upper recording face 3a of the optical disk 3.

In this instance, the upper surface 10b of the turntable 10, objectivelens 12b of the lower optical head 13b, lower restricting means 15b andheight reference pins 11 are set to predetermined heights or verticalpositions H1, H2, H3 and H4, respectively, with respect to a heightreference surface 17 of the optical disk apparatus 8. Here, for example.H1=H3.

Accordingly, the vertical center P1 of the optical disk 3 loaded in sucha manner as described above and the vertical center P2 of the sampleplate 5 are positioned at the same height, and the distance L2 of theobjective lens 12b of the lower optical head 13b from the lowerrecording face 3b of the optical disk 3 is set to a predeterminedoptimum value.

On the other hand, when the upper optical head 13a and upper restrictingelement 15a are moved down together with each other in the direction ofthe arrow mark a by the upper optical head base 14a, the upperrestricting element 15a is contacted with the upper surface 5a of thesample plate 5 so that further downward movement thereof is prevented.Consequently, the downward movement of the upper optical head 13a isautomatically stopped maintaining a fixed positional relationship to theupper restricting element 15a in the vertical direction.

As a result, the objective lens 12a of the upper optical head 13a ismechanically restricted to a predetermined height H5 with respect to theheight reference surface 17, and consequently, the distance L1 of theobjective lens 12a of the upper optical head 13a from the upperrecording face 3a of the optical disk 3 is set to a predeterminedoptimum value readily with a high degree of accuracy. In short,H3=H2+L2. H5=H3+S2+12, H5-H3=S1+L1+L2, and L1=L2.

Accordingly, only if the thickness S2 of the sample plate 5 is adjustedin accordance with a dispersion in thickness of the optical disk 3 suchthat, when the thickness S1 of the optical disk 3 is comparatively greatas shown in FIG. 1, also the thickness 82 of the sample plate 5 is greatcorrespondingly, but when the thickness S1 of the optical disk 3 iscomparatively small as shown in FIG. 2, also the thickness S2 of thesample plate 5 is small correspondingly, then the distances L1 and L2 ofthe objective lenses 12a and 12b of the upper and lower optical heads13a and 13b from the upper and lower recording faces 3a and 3b of theoptical disk 3 can be mechanically set readily with a high degree ofaccuracy with reference to the thickness S2 of the sample plate 5.

It is to be noted that the cartridge 2 is contacted at a plurality ofreference faces 2d, which are individually formed on the opposite upperand lower walls 2c thereof, with the height reference pins 11. Thus, thereference faces 2d of the cartridge 2 are spaced individually from theupper and lower walls 2c by one half an amount Δt of difference inthickness of the optical disk 3 from a maximum thickness of the opticaldisk 3 within a range of difference in thickness S1. Further, if thethickness S3 of the cartridge 2 is increased by the amount Δt by whichthe thickness S1 of the optical disk 3 is increased, then the verticalcenter P1 of the optical disk 3, the vertical center P2 of the sampleplate 5 and the vertical center P3 of the cartridge 2 can be positionedat the same height.

Subsequently, the optical disk cartridge 1 will be described in moredetail with reference to FIGS. 3 to 7.

First, referring to FIGS. 3 and 4, the cartridge 2 in which the opticaldisk 3 is accommodated horizontally for rotation is of the double sidetype such that it can be loaded with either of the upper and lower walls2c thereof on the height reference pins 11 of the optical disk apparatus8. The upper and lower openings 4a and 4b are each formed as anelongated hole which extends along the center P1 of the cartridge 2 froma mid portion of the cartridge 2 to an end portion 2e of the cartridge 2in the direction indicated by an arrow mark b which coincides with adirection in which the cartridge 2 is inserted into the optical diskapparatus 8. The upper and lower openings 4a and 4b are opened or closedby a shutter 19 having a substantially channel-shaped profile when theshutter 19 is slidably moved in either of the directions Indicated by adouble-sided arrow mark c. Two pairs of upper and lower positioningholes 20 in the form of round holes and elongated holes are formedsymmetrically with respect to the center P1 at the opposite end portionsadjacent the end portion 2e of the upper and lower walls 2c of thecartridge 2 In the directions Indicated by the double-sided arrow markc. The upper and lower circular small openings 6a and 6b are formed inpair At the opposite end portions of the upper and lower walls 2c of thecartridge 2 in the directions of the double-sided arrow mark c displacedfrom the outer periphery of the optical disk 3 toward the end portion

Referring now to FIG. 5, such sample plate 5 as described above is heldhorizontally in each of a pair of holding holes 20a of a circular shapeor the like formed horizontally between the upper and lower halves 2aand 2b of the cartridge 2 and between the corresponding upper and lowersmall openings 6a and 6b. The sample plates 5 may be held for verticalmovement within a limited range.

Meanwhile, the sample plates 5 may be molded integrally as part of theupper and lower halves 2a and 2b as shown in FIG. 6.

Referring now to FIG. 7, the positioning holes 20 An the upper and lowerhalves 2a and 2b of the cartridge 2 extend, for example, verticallythrough the cartridge 2, and the upper and lower ends of them areexpanded in diameter and outer axial end faces of them serve as thereference faces 2d. Then, when the cartridge 2 is loaded into theoptical disk apparatus 8 and the top ends of the height reference pins11 are contacted relatively from below with the reference faces 2d ofthe cartridge 2, positioning pins 21 formed at the top ends only of apair of ones of the height reference pins 11 are inserted relativelyfrom below into the positioning holes 20 thereby to effect positioningof the cartridge 2 in a horizontal direction. As described above,depressions having a vertical dimension equal to one half the amount Atdescribed hereinabove are formed adjacent the height reference faces 2din accordance with the necessity.

Subsequently, details of the optical disk apparatus 8 will be describedwith reference to FIGS. 8 to 13.

Referring first to FIG. 8, when the optical disk cartridge 1 is loaded,the optical disk 3 therein is fitted at the center hole 3c thereof withthe center hub 10a of the turntable 10, and the chucking plate 16presses against a portion of the optical disk 3 around the center hole3c in the direction of the arrow mark a. Thereupon, the top end of thespindle 9a is fitted into a center hole 16a formed at the center of thelower face of the chucking plate 16.

The upper and lower optical head bases 14a and 14b have mountedrespectively thereon a pair of upper and lower guide rods 21a and 2lbfor the upper and lower optical heads 13a and 13b, a pair of upper andlower stepping motors 22a and 22b, a pair of upper and lower lead screws23a and 23b, a pair of restricting elements 15a and 15b in the form ofupper and lower vertical pins, and so forth, thereby constituting a pairof upper and lower optical head blocks 24a and 24b, respectively. Thelower optical head base 14b is securely disposed at the height referencefaces 17a, and the height reference pins 11 are mounted on the loweroptical head base 14b. Meanwhile, the upper optical head base 14a of theupper optical head base block 24a is suspended by a plurality ofvertical suspending pins 28 suspended for vertical movement within afixed range in a plurality of suspending holes 27 of a lifting drivingmember 26, a plurality of suspending springs 29 in the form ofcompression springs and a plurality of spring receivers 30.

After the optical disk cartridge 1 is loaded such that the cartridge 2is received horizontally onto the height reference pins 11 while thesample plates 5 are contacted with the lower restricting elements 15b asdescribed hereinabove, the upper optical head block 24a is moved down inthe direction of the arrow mark a by the lifting driving member 26.Then, the upper restricting elements 15a are pressed against the uppersurfaces 5a of the sample plates 5 so that the distances L1 and L2 ofthe objective lenses 12a and 12b of the upper and lower optical heads13a and 13b from the upper and lower recording faces 3a and 3b of theoptical disk 3, respectively, are set with a high degree of accuracy.

Then, the optical disk 3 is driven to rotate by the turntable 10 of thespindle motor 9, and the upper and lower lead screws 23a and 23b aredriven to rotate by the upper and lower stepping motors 22a and 22b sothat the upper and lower optical heads 13a and 13b are fed stepwise ineither of the directions indicated by a double-sided arrow mark d, thatis, in a radial direction of the optical disk 3, under the guidance ofthe upper and lower guide rods 21a and 21b, respectively. Then, spots oflaser beams are irradiated upon the upper and lower recording faces 3aand 3b of the optical disk 3 by the upper and lower objective lenses 12aand 12b of the upper and lower optical heads 13a and 13b to effectrecording (writing) or reproduction (reading) of information onto orfrom the upper and lower recording faces 3a and 3b, respectively.Thereupon, since the distances L1 and L2 are set with a high degree ofaccuracy, the spots of the laser beams are focused correctly on theupper and lower recording faces 3a and 3b, and consequently, recordingor reproduction of information can be performed with a high degree ofaccuracy.

It is to be noted that the lower restricting elements 15b may be formedat the top ends of a pair of the height reference pins 11 so that theymay serve also as the height reference pins 11.

Subsequently, a mounting apparatus of the optical disk cartridge 1 intothe optical disk apparatus 8 will be described with reference to FIGS. 9to 13.

Referring first to FIGS. 9 to 11, when the optical disk cartridge 1 isinserted horizontally in the direction indicated by an arrow mark b intoa cartridge holder 33 through a cartridge insertion opening 32, theshutter 19 is opened In the direction indicated by an arrow mark c inFIG. 11. Then, when the optical disk cartridge 1 is inserted fully intothe cartridge holder 33, this is detected by a switch 34 and a pair ofpinions 35 are driven to rotate simultaneously with each other by aloading motor not shown. A pair of racks 86a formed horizontally on apair of vertical rack plates 86 are driven simultaneously with eachother by the pinions 35 so that the rack plates 36 are slidably movedhorizontally in the direction indicated by an arrow mark e in FIG. 9under the guidance of a plurality of upper and lower slide guides 37mounted on a pair of chasses 41.

Thereupon, a plurality of rollers 38 mounted on the opposite outer sidefaces of the cartridge holder 33 are guided by a plurality ofcorresponding inclined guideways 89 formed in the rack plates 36 while aplurality of other similar rollers 38 are guided by vertical grooves 89formed in the chasses 41 so that the cartridge 33 is moved down byvertical parallel movement in the direction indicated by an arrow mark fin FIG. 10 from a cartridge insertion position P4 to another cartridgemounting position P5 shown in FIG. 9. Then, the cartridge 2 of theoptical disk cartridge 1 is received horizontally on the heightreference pins 11 while the optical disk 3 is received horizontally onthe turntable 10 as described hereinabove.

Referring now to FIG. 12, when the rack plates 36 are slidably moved inthe direction indicated by an arrow mark e, a roller 42a at an end of achuck driving arm 42 is pushed in the direction of the arrow mark e byan end face 36b of one of the rack plates 36 so that the chuckingdriving arm 42 is moved in the direction of the arrow mark e against areturn spring 43. Consequently, a pin 44 at the other end of thechucking driving arm 42 is moved in the direction of the arrow mark ealong a horizontal elongated hole 45 formed in a corresponding one ofthe chasses 41 to move an upper end of a chucking lifting arm 46 mountedfor pivotal motion on the pin 44 in the direction of the arrow mark e,and thereupon, an interlocking arm 49 having an upper end mountedpivotal motion on the chassis 41 by means of a fulcrum pin 47 and havinga lower end connected to a mid portion of the chucking lifting arm 46 bymeans of a pin 48 is pivoted in the direction indicated by an arrow markAs a result, the chucking plate 16 mounted at a lower end of thechucking lifting arm 46 by means of a pin 50 is moved down in thedirection indicated by an arrow mark a from its lifted positionindicated by a chain line in FIG. 12 to a lowered position indicated bya solid line so that the chucking plate 16 holds the optical disk 3against the turntable 10 from above.

Then, when the rack plates 36 are slidably moved fully in the directionof the arrow mark e as shown in FIGS. 12 and 13, this is detected by aswitch 51. Consequently, the loading motor is stopped while at the sametime a lifting driving pinion 53 is driven to rotate by a lifting motor52. The pinion 53 drives a rack 54 formed vertically on the liftingdriving member 26 so that the lifting driving member 26 is moved down byvertical parallel movement in the direction of the arrow mark a underthe guidance of a vertical guide rail 55 and a guide rod 56. As aresult, the upper optical head block 24a is moved down In the directionindicated by an arrow mark a In FIG. 12 from its lifted positionindicated by an alternate long and short dash line in FIG. 12 to itslowered position indicated by a solid line so that the upper opticalhead 16a approaches the upper recording face 3a of the optical disk 3.Then, the lowered position of the lifting driving member 26 is detectedby a switch 59, and thereupon, the lifting motor 52 is stopped. It is tobe noted that the guide rail 55 is securely mounted vertically on thechassis 41 or the like, and a thrust bearing 57 is securely mounted onthe lifting driving member 26 and is fitted without a play on the guiderail 55 in such fitting as dovetail fitting so that it is slidably movedvertically. Meanwhile, the guide rod 56 is securely mounted verticallyon the lifting driving member 26 so that the lifting driving member 26is slidably moved vertically without a play by means of a thrust bearing58 mounted on the chassis 41 or the like. When the optical diskcartridge 1 is to be unloaded, the optical disk cartridge mountingapparatus operates reversely to that described hereinabove.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit and scope of theinvention as set forth herein.

What is claimed is:
 1. An optical disk apparatus comprising:means for removably loading in position an optical disk cartridge in which an optical disk having a first thickness and having a pair of recording faces formed on the opposite surfaces thereof is accommodated for rotation, the optical disk cartridge having a sample plate of a second thickness determined in accordance with the first thickness of the optical disk and disposed at a position at which said sample plate does not interfere with the optical disk; a turntable of a spindle motor for removably receiving thereon the optical disk in the optical disk cartridge loaded in position; a pair of optical heads mounted for individual relative movement toward the recording faces of the optical disk received on said turntable; and a pair of restricting means for contacting with the opposite surfaces of said sample plate of the optical disk cartridge to mechanically restrict the distances of said optical heads from the recording faces of the optical disk.
 2. The optical disk apparatus according to claim 1, wherein the first thickness is equal to the second thickness.
 3. The optical disk apparatus according to claim 2, wherein said optical disk and said sample plate are disposed in the same plane.
 4. An optical disk recording and/or reproducing apparatus for recording and/or reproducing data on an optical disk having upper and lower surfaces bearing recording areas, said disk rotatably housed within an optical disk cartridge, said apparatus comprising:a turntable for receiving said optical disk; a sample plate in said optical disk cartridge having a particular thickness corresponding to the thickness of said optical disk in said optical disk cartridge; a lower optical head for accessing the lower surface of said optical disk; a first restricting means fixedly connected to said lower optical head for receiving a lower surface of said sample plate whereby a distance between said lower optical head and said lower surface of said optical disk is fixed; an upper optical head for accessing the upper surface of said optical disk; and second restricting means fixedly connected to said upper optical head for engaging an upper surface of said sample plate whereby a distance between said upper optical head and the upper surface of said optical disc is fixed.
 5. A optical disk apparatus as set forth in claim 4 wherein said second restricting means is moveable normal to said upper surface of said optical disk. 